The mathematics I use most is basic arithmetic, when doing one-off data processing runs. Mostly used in estimating how long things will take to run (e.g. it took 20 minutes on this sample of one thousandth of the data, how long will it take for the full dataset?), or estimating storage requirements.

Currently I'm working in medical imaging with large 3d data sets so linear algebra plays a prominent role.

Almost none in business apps. There's some calc and geometry in graphics. Unless the business demands it, the software isn't going to need math. Yagni. If the business can run on a pocket calculator, every last pc will disappear in pursuit of the dollar. The same goes with math.

Linear algebra: My work tends to be mostly visual; either computer vision or graphics.

Linear algebra is indispensable when working with any sort of graphics.

Graph Theory

Basic design of any solutions become real graceful.

stats and formal logic.

linear systems